Topband: Shunt feed series capacitor

[EA2LU Jorge Daglio]

Hi folks, for the records, I have 90 feet high triangular Heliax tower 3 feet per side.
It was shunt feed before, but I ask Earl K6SE to recalculate the optimum tap
point because I was not satisfaced with the results. Earl made a great
job modeling it on EZNEC, and his results are exactly as expected.
He propossed: Tap at 25 feet (with poor ground system) and seriers
capacitor  585Pf.
I put (I climb tower at 0 Cº celcius)Tap (RG213, center/braid togheter) at 25 feet
and 500Pf series capacitor...
Results: 1:1 SWR at 1870Mhz with full caps
As you can see I need some more capacity, like Earl advice.
Question; I have very good quality 500Pf vacumm cap, but it need some
more capacity, to put the antenna on QRG. ¿Could I add 100Pf  fixed
from 100Pf 15Kv doorknow capacitor from my "junk box"?
I have 10 of it,  then I could make a packet of it.
Power out, would  be full from an Alpha 91b.
Any help would be very welcome, thanks you very much.
73 de Jorge EA2LU