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__':
    for _ in range(int(input())):
        n = int(input())
        a = list(map(int,input().split()))
        m = max(a)
        b = True
        for i in range(len(a)):
            if a[i]!=m:
                b = False
                break
        if b:
            print(-1)
        else:
            for i in range(len(a)):
                if a[i]==m:
                    if i==0:
                        if a[i+1]<m:
                            print(i+1)
                            break
                    elif i == n:
                        if a[i-1]<m:
                            print(i+1)
                            break
                    elif a[i-1]<m or a[i+1]<m:
                        print(i+1)
                        break
        
