Check below photos, could you tell the baby seedlings between mini Sinn. and Smithiantha ?
Almost nothing to do during hot summer time (the truth is if I do, I do it in vain), therefore I normally sow seeds of Gesneriads because the baby seedlings are easier to handle at this moment (only my personal opinion). Just two key points, to avoid direct sunlight and stuffy environment. After the growth for 2 or 3 months, the seedlings will be big enough to be repotted in the autumn which is the temperate season for growing up.
Back to the topic, the answer is the above is mini Sinn and the below is Smithiatha. :)