1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

if __name__=='__main__':
    t=int(input())
    for i in range(t):
        n=int(input())
        a=list(map(int,input().split()))
        ind=[]
        _max=start=-1
        for i in range(0,len(a)-1):
            if a[i]>a[i+1] and a[i]>_max:
                _max=a[i]
                start=i
            
        for i in range(len(a)-1,0,-1):
            if a[i]>a[i-1] and a[i]>_max:
                _max=a[i]
                start=i
    
        if start==-1:
            print('-1')
        else:
            print(start+1)
        #print(ind)