It depends on what the REAL value (not the displayed value) of the HML (also applies to HLL) is, and what the speed of the weapon is before and after the SSI addition.
The DISPLAYED HML is a DERIVED value. It's determined by multiplying the actual intensity by a factor based on the weapon speed - a weapon speed that is determined by the weapon's base speed, modified by SSI. And, it's display doesn't show more than 100%, even if the final number is well over 100%. The idea is to make it to where the leech-over-time for the same intensity remains the same, by having a bunch of small leeches for the fast weapon, compared to 1-2 large leeches over the same period.
As a result, some extremely slow weapons can get imbued with 30% SSI and not drop below 100%; others might drop from just 5% SSI. It depends on what the real intensity is, and the weapon speed. And, since those changes almost a decade ago, Leeches trigger EVERY swing - the % displayed is related to the amount of damage leeched, not the chance of a leech (which was what it was from AoS to a year or two after ML).
If forget which is which (HML & HLL - Stamina leech is still straight up 100%), but one of the leeches gives 30% x (random, 1 to displayed value) damage done back, while the other uses 40% of the damage done as the base.
Note that the actual intensities, before the speed is factored in, ranges up to 50% leech at 100% intensity, before being overcapped. This is why, prior to the changes to HML & HLL, the Soul Seeker minor artifact from ML displayed 40%/40%/40% (80% intensity for all three leeches), but after the changes to factor in weapon speed and SSI, now displays 30% for HML & HLL (still 80% intensity, but the final weapon speed results in the displayed value being the real intensity's value x 0.75).
Some of the really slow weapon speeds, have a multiplier over 200%.
For the displayed value to stay 100%, the multiplier has to still be over 200% after the SSI, or the Leech be overcapped intensity to start with, or both.
Your best bet is to go to Test Center (if you have the weapon already, copy a character there WITH it - otherwise craft a reasonable substitute there with the runics) and modify it there, to see what happens.
