Is this considered sufficient by most people?
As I realized today, a stationary white flag to cover a tow vehicle on the racing line on the other side of a blind hill is not easy to spot. I went back to look at my video and, in the midst of a pack of 3 or 4 guys, I did indeed miss it, thinking that stationary white square was a uniform or one of the plain pieces of metal used to shade the corner stations. Only after passing one tow vehicle headed onto track with no lights, and seeing the second vehicle around the aforementioned blind corner did I slow, get passed for my trouble, and then come over the next hill to see a FCY. In the end, it all worked out fine and made no difference to the final results, but I was worried about what could have gone wrong.
Am I off base?

Having been a corner worker prior to racing I will weigh in.

If the FCY had not yet been thrown, and you were coming at me (as a corner worker) at a high rate of speed, I would try to shake the white flag in a manner to make it more visible to you.

Here's the best still I could get of it. Fundamentally, this corner station is out of your site line most of the time, so I'll have to make a better effort to look at it during this busy part of the track:

I agree with Kurt, I will often shake or "rock" the flag if people are coming up on a vehicle that was just dispatched on track and had no previous station as warning, or if they are just flying and I want them to know hey slow vehicle/safety be ready.

COTA.....well their flag stations suck end of story. Even for F1 I think so many are way off and won't be seen. That is a problem with these level one tracks is that the thinking is for F1 and the equipment that comes with them such as the lightboards and stuff. After that, it seems to be moot point.

I have literally been at some tracks, mostly FIA level 1 where I question wtf am I doing here? No one will see this stuff.

The light boards are great for visibility, but there's always a delay until they activate. I definitely prefer having live flaggers where they're easy to see, assuming they're in a safe position. Actually all the colored flags are pretty easy to see even way off line, but whites are damn near invisible and the GCR only talks about a waving white for last lap. Might make sense to codify the excellent practice of waving it or adding a yellow at the location of the slow vehicle. Heck, I'd be OK if it wave just replaced with a yellow when the slow vehicle is on the racing lane.

The white is also an FIA rule, so it isn't limited to just SCCA and North America. What has been picked up by IMSA and Indycar, since they use the same race control communicators who have guided some of their rules,

Forgot the exact amount but I believe it was for vehicle moving at 1/2 or 1/3 speed it becomes a waving white, along with any Emergency Vehicle on track. That way it gives you differentiation between between a car that is off pace vs way off pace/EV.

As for light boards, I do not have a problem with them as long as we retain control of them on the turns. Some systems it is controlled or more controlled in the tower than on the turn. I actually enjoy light boards as a driver, and sometimes even as a flagger...flagging can get exhausting. But I still want control. I want to be able to control the frequency of say a waving yellow and especially a blue flag. Most of the systems have the blue as a simple flash sequence all the time and that doesn't sit well with me. As I say when training new flaggers, you are talking to the drivers not just showing them a flag. Your movements and body language help convey your message.

I've long been an advocate of waving or shaking white and debris flags when an urgent condition exists. This should become SOP ASAP.

Bob , Some flags are Mandatory or Direction flags and some are Advisory flags. That being said, I think any waving flag draws the attention of the driver. It seems to me that a Yellow flag and the white can cover the scene. Waving Yellow really increases the warning and direction of no passing. While the white covers the emergency vehicle.

I major concern from viewing youtube@ videos, is that the leaders in most cases are not slowing or at least lifting. Back in my day I can remember using Black Flag ALL. and having conversations with the drivers. On their race time. Yes, today's management is different and needs to be.
I just hope we never have a race car hitting an emergency vehicle.
(Yes I have seen ALMOST that happen)
Shut Up John .... Ok

You never want to do a waving surface flag. Bikes do it and lets just say it doesn't look like a surface flag.

As for the white always remember it is only for when a vehicle is in motion, slow or EV vehicle. Once the vehicle stops it becomes a yellow. Many flaggers often have the white with the yellow but that is wrong. Also remember yellow flags are not just for vehicle on track or safety personnel on the ground, it also means be prepared to stop aka bring your car to a greatly reduced speed while under control.

Club racers respect waving yellows more than pros which is sad. Still we have had calls especially at the runoffs of drivers not respecting the waving yellows as much in incident zones.

I will never forget Martin Thake's English accent telling everybody on the INDYCAR safety team's radio "Control, car # 6 has just run under the back of safety 1!!". That was Mario Andretti, in downtown Detroit, in the early 90s. It never occurred to him to lift just because of a white flag! Safety 1 was a pickup. At the next race , a hydraulically operated drop down "Andretti Bumper" was installed on the safety trucks. It skimmed along about 2 inches off the race surface to prevent a recurrence!