How Much Tension on Inner Forestay?

[Chainplate]

My ketch's very heavy Selden mast was rigged by the yard that built the boat without forward lowers. We do have Profurl roller furling for both the headstay and the inner forestay. The mast is rigged with running backs but we typically only use them when flying the staysail and that's usually only when there's heavier weather.

How much tension should be on the inner forestay? With the roller furling in place, how would the tension be measured? Or should it just be 'tight' or 'very tight'?

Thanks for your input.

Fair winds and calm seas.