I have a similar problem to last year - it is now worse! I moved to my present small house in August 2 years ago. In the front (small gravelled area) there was a lacecap hydrangea under my kitchen window, which was fairly compact with no flowers. The following year it bore beautiful white/pale blueish lavender flowers and had become quite large. I pruned it as advised - in Spring above a bud. The buds were quite high on the stems. This year it has become enormous and is almost blocking my kitchen window.
I would prefer not to sacrifice the lovely flower heads but it is really just too big. The stems are very long and spreading outwards as well as up. I really cannot dig it out - I just want to reduce the size! I would like to do this when it has finished flowering if possible as it is taking up so much room and starting to look messy/untidy. Any suggestions please?