Medical textbooks frequently suggest 1mg as the informal maximum bioavailable dose that you can expect to be absorbed sublingually for other drugs, sometimes as low as 0.5mg
When higher doses are needed, like can be in the case of nitroglycerin for the heart, the labels suggest waiting 5 minutes then applying again vs applying more at once
And that's with dissolving tablets or sprays designed for this purpose, so not worth doing with a min tablet designed for slow release in the digestive tract, but possibly a reasonable strategy with the liquid
IMO this implies that you shouldn't bother with more than 1mg min liquid sublingually at a time - if you want more a better strategy would be to wait e.g. 15 minutes and apply again
(and even if you could absorb more, there's safety concerns that peak plasma levels will spike very high)