Play with the pitch a bit til you find one you can hear well. Lower may be better...
Óh yes, that proposal has a kind of scientific base.
When you transmit a number of dots, your pitch has sidebands on the "distance" of the ditfrequency and multiples of it. They are mirrored against the zero freuency line and the mirrored may be on the same frequency als lower harmonics of the sidebandfrequency.
Strange things happen in your mind when
a) they are exactly half way, such that your brain detects the spectrum as a modulation frequency of double the value of the original modulation speed.
b) they are on the same frequency as the original lower harmonic sidebands, That smoothens the lower sideband. You obtain nearly the same effect when you modulate not with a block but with a triangle or sawtooth envelope. That will certainly increase your copy speed.
73 from hell where the costs of heating are all for free.