Stripe ACH: How to calculate application and stripe processing fees

Question

I am planning to use stripe connect to accept payments on behalf of others for us based renting property solution. I am creating customer for the tenants and connected custom accounts for the landlords, then creating charges to transfer money from a tenant account to a landlord connected account. I have used plaid to update the external bank account with stripe while creating customer accounts on stripe.

I have some confusion over the platform/application and processing fees. As a merchant, how much fees needs to be collected from tenant.

Currently, I am using the below code to charge.

$app_fee = 0;
if($rent_amount >= 62500)
{ 
    $app_fee = 500; 
}
else
{ 
    $app_fee = (round(((($rent_amount / 100) * 0.8) / 100),2) * 100); 
}

$charge = \Stripe\Charge::create(array(
'amount' => $amount,
'currency' => 'usd',
'application_fee' => $app_fee,
'description' => 'Example charge',
'customer' => '######', 
'destination' => '#######', 
));

Any help would be appreciated.

Thanks