I just read that one and OMG I love it !! the drawing so flawless, the atmosphere it gives : so nice! everyone is back on the track ! I think according to the TV serie and how the relationship between the characters evolves, and especially the relationship between Relena and Heero... this plot would occur just after the end of the TV serie ! because of different hints (like the gift Relena received and what she did at the end of the TV serie with a certain... paper...) you can find the same elements in this manga, just like it would follow the TV serie plot. Moreover the drawing and the atmospehre around heero and relena in Blind Target just confirm perfectly what happened between them at the end of the TV serie and show some logical developpement after what happened in the TV serie!
I would even say that this ground target is much more following the TV serie than the OVA themselves... the OVA don't take into account what happened at the end of the TV serie between Relena and Heero for example... they had some strong connection, and heero really showed his emotions, such things we don't really find in the OVAs contrary to Blind Target following closer the developpement of the TV serie !