We used some largeish target numbers on an FT course last Sunday. Size was approx 100x100mm and all were bright colours. I thought they worked very well at directing the shooter onto the correct target. I know you said earlier that target numbers are not always placed at the target, but when they aren' t they must be placed in front or behind the target - in which case you can use the target number to direct your line of sight.
With a lot of HFT targets now there isn't much plate around the kill or most of the plate is obscured. Once the target is shot up you end up with a grey mass around the kill and not much paint, dayglo or not.
I have sympathy for your condition but if the target cannot be seen properly through a decent scope like your Lightstream, I think you will have problems shooting any knockdowns, whatever the paint job.
Worth having a trail at your club though as suggested by Scooby to see if it helps.