Hi. I've bought a fairly big (400mm x 1500mm) towel radiator, which will be
water filled (attached to CH), so quite heavy.

There are 4 supports which came with it. I think they are standard towel
radiator supports. They include 4 tubes. Each tube is completely open at
one end and closed at the other end. The closed end is drilled with a hole
for a screw to pass through, so the tube is screwed end-on to the wall.
(That doesn't sound clear, but if you've used them, you'll know what I
mean!). The radiator is attached to the tubes with some other bits

My wall is fairly sound - plaster over brick - but my concern is the
leverage on the tubes. It will tend to bend the tubes downwards as the
relatively soft plaster will be crushed by the leverage. If I were putting
these on tiles, I think the hardness would provide sufficient support, but
I'm not.

Has anyone used this system and found problems? Or am I worrying over
nothing?
Do I need additional support for the tubes (e.g. metal plate on the wall
surface for the tube to press against)?

Cheers