You might be underestimating the potency of my horseradish.. Lol
Well, yes and no. You just want to add the amount of horseradish that you like. Not so much that it's overpowering, but enough that it kicks. Add a little, taste it, then add more until it tastes right.
I make my horseradish in a food processor, and I do it all kinds of ways. If I want it really pungent I'll cut it into cubes and blend it with a little water (1/4 to 1/2 a cup or so) and a dash of salt for up to 3 minutes until it's almost a smooth paste, then add a couple of tablespoons of vinegar and pulse blend for another 30-60 seconds. That's gonna be pretty hot... what with waiting 3-4 minutes before adding the vinegar and with having all those cell walls broken down about as much as possible by making a paste.
Sometimes, after cutting it into cubes for the food processor, I'll make a mixture of about one cup of 50/50 water and vinegar. I'll pour a little plain water into the food processor right from the start, adding more of the water/vinegar as I go as needed. I rarely use the whole cup of liquid. But I blend until the horseradish is smooth but still chunky, like minced garlic. So, two things, adding the vinegar from very early on, and leaving it more chunky, both creates a still pungent but rather mild horseradish.
Most often, though, instead of cutting it into cubes I'll just peel it and then feed it into the food processor onto a fine grating blade to grate it from the start. That'll wake it up and cause those isothiocyanates to be released quickly. Then I'll swap the grating blade with the chopping blade, which I take 2-3 minutes to do, then I'll add some 50/50 water/vinegar, and salt, and pulse blend for 30-60 seconds, scraping down the bowl a few times. That results in a pretty potent horseradish.
It's mostly about how finely chopped it is, and how soon you add the vinegar. If really mild is a 1, and hot as it can get is a 10, I like mine about a 7 or 8.
