Does the rank range filter round to integer ranks?

The Custom game dialog has settings for “Minimum ranking” and “Maximum ranking”. That seems clear: setting e.g. 1d to 3d includes everyone who’s a 1d, 2d, or 3d.

On the settings dialog for Quick match finder, there’s an “Opponent rank range” field which works slightly differently. Instead of setting an exact rank, you set the minimum and maximum rank difference from your own (-3 to +3, -1 to +1, etc.).

Does anyone know if the “Opponent rank range” uses your exact rank or integer rank as its baseline? For example, say I’m at 2.8d, so my rank appears as 2d. If I set my opponent rank range to -1 to +1, will the range be:

a) 1.8d to 3.8d; or
b) 1d to 3d

(a) would include a few 1 dans, all 2 dans, and most 3 dans.

(b) would capture all 1 dans, 2 dans, and 3 dans.

a) should be 1.8d up to 4.8d. If you set it to ±0, I would expect it to capture your rank (2.8d to 3.8d)

Btw. I don’t know the answer.