Steven,

When you use a backplate tap on the engine I would not try the nonreturnvalve in the connection between the tap and the tank in the first place.
The pressure can be too much for the tank and than you have really troubles.

When using a tap on the backplate I would try a restriction between this tap and the tank in the first place.
In the tank the result will be the average pressure and that can be 3,5 PSI, 50 % of the 7 PSI, I do not know for sure but I think.
This pressure is more than enough , good for a fuel height above te plane of about 3 meter, 10 feet.
The restriction prevents the pressure drop too fast when idling the engine.
The position in the air, nose up and engine idle, will normally not be long!

Provit of this set-up is the presure will drop to zero after a short time the engine stops.
A non return valve will keep the pressure high in the tank so the tank can leak fuel and for sure when the tank is full and the temperature rises..

I do not have experience with this set-up, but it seems to be more logic. Maybe other members have advice?

Cees