Handbrake not efficient enough for IVA

[Wain]

I have recently failed the IVA, one of the points was due to the handbrake not being efficient enough. I have Wilwood calipers, but with the handbrake on the car can still be pushed. I have spoken with the supplier who advised this is normal as the handbrake does not have the leverage to sufficiently apply the handbrake. Has anyone else had a similar issue? has anyone else had to create a linkage mechanism to improve handbrake efficiency?