Every time I make an adjustment to something about the portal setup, such as changing the specs for the portal filter, the portal becomes 1 or more points shorter. I have to then use the inspector to increase its height by as many points as it changed. Which means I have to memorize the height before making the change if the positioning is critical.
Guides are not set to snap to anything, in fact guides are turned off.
If I increase the number of rows, I expect to see the height change, by adding one row equal to the height of the others, or vice versa. But I see no reason why the size of the portal should become 1 or more points smaller just because I redefine the portal filter.