There is no such thing as speakers with "good throw" :-)

Volume will attenuate at the same rate (inverse square) no matter what the speaker. Some speakers, of course, are more directional, but that's not the same thing.

Often the best thing to improve the coverage at the back is to get the speakers up high - well above the audience's heads, and facing slightly downwards. That way the sound isn't absorbed by the audience as much, you're not losing half your power up to the roof, and you don't have to worry about delays. Of course, adding height isn't very practical with the L1...

If you do add smaller relays further back in the room, it often causes more problems than it solves. Cabling is a pain. You'll need to add delay, and although that sounds simple in theory, it may give problems in practice - the optimum delay can be easily calculated - 1ms for every foot between the front and delay speakers - but in practice the formula is only right for one location in the room. In an echoy room (in particular if there's slapback echo off the back wall) you could easily make things worse.

But go ahead and try it - get a delay line, measure the distance between front and delay speakers in feet, dial in that delay in millisecond. Then add on 10 milliseconds for the "haas effect" - a bit of psychoacoustics - the extra 10ms delay means that the audience at the back will hear the quiet sound from the front speakers before the louder sound from the delays - the overall effect is that the brain is fooled, and the sound "appears" to have come from the front rather than the speakers at the side!