The issueing of Schengen C-Visas, is on the one side restrictive, but on the otherhand practical.
So it is a combination of how the visa was used in the past and the need in the future.
In your case, you have allready fullfilled step 01 (properly used a single business visa).
For the next application apply for a multiple entry business visa (checkbox field 24) togeather with a letter from your employer stating that they want you to visit them many times per year. This should get you at least a multiple entry visa for 1 year.
The next application (step 02), when the previous one was not missused and the need still exists, will probably lead to a visa that is valid longer than 1 year.
Multiple entries (Page 76)
When a multiple entry visa is issued with a period of validity between 180 days (6 months) and 5 years, the duration of authorised stay is always 90 days (per 180 day-period). This also applies in cases where the visa is issued for the purpose of transit.
Visas allowing for multiple entries may also be issued with a validity of less than 6 months.
Multiple-entry visa should, in principle, not be issued to first-time applicants.
Under the following circumstances a multiple-entry visa (including for the purpose of transit) shall be issued:
An applicant having proved his integrity and reliability, in particular, through the lawful use of previous uniform visas or visas with limited territorial validity (issued in accordance with Article 25(3) of the Visa Code, see point 8.5.3) issued by any Member State, his economic situation in the country of origin and his genuine intention to leave the territory of the Member States before the expiry of the visa applied for and, who proves the need or justifies the intention to travel frequently and/or regularly, in particular due to his occupational or family status:
Recommended best practice with regard to the harmonised practices for the issuing of multiple entry visas in a given location: With a view to harmonising practices as part of local Schengen cooperation, Member States should discuss the length of validity of multiple entry visas to be issued to persons eligible for such visas and the progressively increasing validity of such visas in accordance with the below guidelines, which may be adapted to local circumstances:
- persons having lawfully used previous Schengen visas issued within the previous year: a multiple-entry visa with a validity of one year;
- persons having lawfully used a multiple entry Schengen visa, in the previous 24 months: a multiple-entry visas with a validity of a minimum of two and a maximum of five years.