Replied to this last night, but the forum choked and dumped my post.
The 3839 tick default value is to accommodate theoretically possible time signatures of x/1, where the beat length is a whole note - i.e. 4 x 960 = 3840 (ticks numbered 0-3839).
In your case, if the MIDI is quantized, you don't have to mess with the separate selections. You can just set the Min/Max beat values to 1, and the tick values to 0, and you'll catch all the downbeats.
If it's
not quantized, and events can fall both early (i.e. late in beat 4) or late (i.e. early in beat 1), then you'll have to first select for beat 1 with a range of maybe 0-40, and process that as needed. Then re-select the whole clip/range, re-filter for beat 4 with a range of 920-959 (or 920-3839 - the extra range doesn't matter), and repeat the processing.
Don't let the "busyness"of the filter dialog intimidate you. Just realize that it defaults to including all events with all parameters, and you just have to focus on restricting the range of the one (or more parameters) that you care about. For example if you also want to make sure that you affect only the C3s on the downbeat (e.g. Kick drum in a typical drum synth, you could add that restriction to the Note range. Be aware, incidentlaly that you can hit keys on your controller to enter note values, rather than typing them in.
Sometimes it's easier to limit you selection
before applying the filter. In the above case, for example, you could open the drum track in the PRV, and click the key corresponding to the Kick, and then filter that limited selection for the downbeats.
There are more - sometimes easier - ways to make a special selection, and there may often be CAL files that can help, but the Event Filter, (and its bug brother, Process > Interpolate), can be very useful in certain situations.