The tender amounts are subjective. The parent team essentially decides how much the player is worth and provides a qualifying offer sheet based on what "level" they think his value is (1st round / 1st & 3rd round), but it also has to be at least at the level of the player's original draft selection and something like at least 120% of the prior year salary ... I kind of forget now.
Simply there are rules about it ...
The general base level of money is determined by the league in the cba and it is based on accrued seasons and/or original round selected.
If the Redskins wanted Sam Shields they would have to not only match the tender level (qualifying offer sheet) but likewise give draft pick compensation.
That's if GB decided not to evoke it's right of first refusal. That just means they can match an offer their player receives from other clubs. If GB wanted to match the Skins offer they could.
But beyond that:
A team cannot exercise its right of first refusal pursuant to a sign-and-trade agreement.
When a team exercises its right of first refusal to keep a restricted free agent, it cannot trade the player for one year without the player’s consent. Even with the player’s consent, for one year, the player cannot be traded to the team whose offer sheet was matched.
Any player for whom a team exercises its right of first refusal may not be traded before the later of (i) three months following the date the contract was signed and (ii) the December 15 of the salary cap year in which the contract was signed.