Road long is some what shorter, distance between pulleys,
than mountain long cage.

wrap is (big+big) minus (small+small), it is the wrap up of slack ,
that has the distance between the 2 pulleys needing to be greater.

not much significant issues in erring towards too long, .. having too short a cage,
but having sufficient chain length, means some slack in the chain
is not tensioned by the return spring that rotates the pulley cage...

when combining small chainring and the smaller cogs on the wheel.

So, why not go with the longer cage ?

But you are only adding 2 teeth.

since the new chain types have lower tolerance for just adding a link,
It's a good time for a new chain,
and make it a link longer when you install it.

if that won't work well .. then, buy a longer cage derailleur.