mini zap cat yam 20hp prop selection help please

[supremesoundz]

hi got a ceasar mini cat http://www.ceasarmarine.com/ceasar_mini_cat.aspx

it has a yamaha 20 hp 2 stroke motor on it with the standard prop?

ive seen ppl with t totsi 25 and 30 on them mounted 30 mm up off the transom n run fully trimmed out ive got mine sat fully down and trimmed out last hole on the pins it just prop spins, it also does this on the next one in and a bit just b4 getting on the plane and on turns on the next in so im down on the second one out from in fully.

it has the std prop 9 7/8 x 10" im getting 44.7kmh by sat nav on rolly water

ive seen a 18hp with a 13" pitch im assuming it is doing 52kph

and a 30hp with a 15" im assuming thts pitch prop doing 72kph

just want some info as to positioning where should my cavitation plate sit in relation to the top of the tunnel (floor)

and what sort a prop should i be looking for ive seen cuped or semi cleavers are good on tunnel boats n cats as the prop is only just under the surface any thoughts or suppliers in the uk much appreciated