Refitting a (different) heater to my CE.

It sits OK on the two brackets on the bulkhead, but when I swing the
heater up to meet the two captive plates under the bottom rail, the
self tappers don't line up with the fixing holes and they are quite a
way out.

Its not side-ways alignment - the discrepancy makes the holes 'too far
away' from the bulkhead by a good 1/4"

Can't see what needs 'adjusting' to make them line up.

Anyone any ideas please?

Thanks

P