A change in position will usually lead to different sensations as you start to use different or more of a certain muscle so allow a week to two to let your body adjust and whilst on the trainer it’s s great way to where your body is on the bike , do you feel planted on the saddle , us the pedal stroke smooth are your arms/shoulders tense etc have you got good posture lengthening the spine , see what feedback your body gives you after making changes and trust it.