This looks like somebody wants to add two pilot modifiers to one attack value, and I have to say that SA-11 is really messy with the wording. SA-18 does seem to be written better with less unnecessary text.
Even so, in both cases we are dealing with a replacement value. Because the wording of the two cards is more or less specific about what is being replaced and how, I'd say that SA-11 would use the friendly unit's modified value as is and not add any modifiers of it's own, this is assuming the friendly unit actually has a better attack value and still has to qualify with a clear line of fire to the target.
SA-18 does not require a clear line of fire, but the shared attack value must be the unmodified number printed on the dial and I might suppose that the attacking unit can not add any modifiers of it's own. This is again assuming the unmodified value being shared is still superior to the actual attacker.
It is hard these days to say for certain what WK actually intended with these cards, but going with them as worded without interperative guess work is the best way.
*** Yes a special purpose Rules thread would be nice, though 600 posts on one thread will make some wonder which Rule or how many rules need so much attention. Then again, even on the WK site with a whole forum just for Rules questions, nobody ever searched to see if their question had already been asked and answered by another.
We have a good community able to explain the rules to new players. My comments above are just an opinion on how the cards should be used. Personally, I think all Situation Alliance cards should be used to start a bonfire.
GC