ruff one more h to prepare for trump coup if RHO is holding spade jack fourth
Yes this is correct I think. However, if you think LHO has six hearts, then its right to hope for 3-2 spades, or to play RHO for at least 4 diamonds and not trying to risk ruffing the heart.
At the table LHO didn't tap dummy at T2, so although trump were 4-1 I was able to make this without any problem.
You open 1S in 4th seat and LHO overcalls 2H. Pard makes a questionable splinter and you end up in 6S.