When you have vacation and are awarded a reserve line, what your awarded vacation conflicts with is mostly irrelevant. You will have the awarded number of days (7, 8, or whatever) times R-day value (4:33hr per day for my jet) as a minimum. You can take more days if you want, using the formula in the CBA, but you can't take less. Then they reconstruct your reserve line, minus the days of vacation you used, and not on those awarded days. Take 7 days, and for a five week month, you will still have 12 days of reserve (8 days for a 4 week month.)
VTO is worse as they take your vacation at 6 hr per day, and then build a line around it, even if it's all R days. The only way you can take less days than your award is to get awarded a flying line and conflict with less flying, if possible.