PA3GUO Dag Henk, to my surprise the difference between the "bare" LNB in the upper picture and the patch/LNB/rocket-lens combination in the lower picture, was close to zero!. I checked the QO-100 beacon SNR via SDRuno (SDRPlay RSP2pro) on both systems with short interval and found very much the same SNR (there is always a kind of QSB...).
I probably was lucky to find at first try the optimum focal point position for the patch/lens, so you might have to play with this as mentioned by others as well.
Note: I used two identical LNB units in this test. Both are unmodified (just one having the 22mm hole in the front cap) and from a batch of six pieces they all had very close SNR performance.
As a general remark on the 22mm hole drilling: try to keep it centered very well to get the patch-waveguide tube inserted centered with the LNB waveguide. With the drilled hole offset, the LNB will be mounted at an angle, looking at least ugly...