Any recommendation from a tank manufacturer is developer independent - it says nothing about the chemical capacity of whatever "soup" you are using, but rather deals only with whether or not the volume of your working solution is enough to cover the film and within the range that will permit the right sort of agitation and not flow over and out of the tank.

The developer manufacturers' recommendations deal only with the chemical capacity of the "soup" you are using, and are tank and reel independent. If you choose a dilution and prepare a working solution based on the minimum quantity of developer concentrate or stock sufficient to ensure appropriate chemical capacity, then the volume of working solution that results may be either:
a) too little to cover the films and ensure appropriate agitation,
b) appropriate for your tank, or
c) too much to fit into the tanks and ensure appropriate agitation.

When the numbers are really close, I would tend to increase the strength of the dilution slightly to make it work, but there is probably enough safety room built into (in this case Ilford's) the recommendations to protect you.