  Allowing for the conical shape of ultrarelativistic blazar jets with opening
angles of a few degrees on parsec-scales we show that their bulk Lorentz
factors and viewing angles can be much larger than the values usually inferred
by combining their flux variability and proper motion measurements. This is in
accord with our earlier finding that such ultrarelativistic (Lorentz factor,
Gamma > 30) conical jets can reconcile the relatively slow apparent motions of
VLBI knots in TeV blazars with the extremely fast flows implied by their rapid
gamma-ray variability. This jet geometry also implies that de-projected jet
opening angles will typically be significantly underestimated from VLBI
measurements. In addition, de-projected jet lengths will be considerably
overestimated if high Lorentz factors and significant opening angles are not
taken into account.
