Not quite, Sanction refresh is always 1/tic (up to a % of your total MP, based on Besieged level).
Game seems to check for upkeep costs before any refresh/regen effect.
Let's assume you start with 1 MP: latent kicks in and it drains the mp.
Next tic you have 0 MP, latent does not activate, so no MP drain, Sanction refresh kicks in and you have 1 MP.
Rinse and repeat.
With Sanction and RDM's refresh you might be able to get the haste full time, otherwise only 1/2 the time as stated.
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