So, did the 5 element Yagi-Uda work with 4 elements only? I know the World wants to know!
Yes, it does work. First I checked with an antenna analyzer the new setup (using dir2 and dir3 as dir1 and dir2 respectively) and I measured a nice 1.1:1 SWR at 144.3 MHz.
Then I mounted it outside and tried some real-life contacts. SWR was 1.2:1, probably increased because of the metallic fence nearby the antenna.
Either propagation was better than one month ago or the theoretical 1dB extra gain on my other 4el beam did help a bit: best DX at 227km with 50W SSB. Not bad for a beam on a balcony!